Geochemical method of soil surveying for hydrocarbons



blue.

United States Patent 3 254,959 GEOCHEMICAL METHOD OF SOIL SURVEYING FOR HYDROCARBONS Wayne S. Fallgatter and Bennie Heinze, Tulsa, Okla., as-

signors to Cities Service Research and Development Company, New York, N.Y., a corporation of New Jersey No Drawing. Filed Nov. 27, 1962, Ser. No. 240,770 11 Claims. (Cl. 2323Q) This invention relates to geochemical exploration and in particular to a method of analysis of earth samples to determine the proximity of petroleum deposits.

Various methods have been used to detect the presence of petroleum constituents in surface or underground formations in greater than normal quantity. Such anomalies are taken as an indication of the proximity of a petroleum reservoir or other concentration of petroleum type hydrocarbons. By correlating the relative amounts of petroleum constituents present in the earth samples, such as soil or rock samples, with the locations from which the samples were taken, it is possible to ascertain the location and proximity of petroleum deposits.

In one method, described in US. Patent 2,451,883, the organic constituents of an earth sample are extracted, and the fluorescence of the extract is evaluated under ultraviolet light. As pointed out in copending application S.N. 94,168 now US. Patent No. 3,149,068 of Bie-derman and Heinze, while petroleum constituents especially the lighter aromatics normally found in petroleum fluoresce strongly in the light blue range under ultra violet radiation, numerous other organic compounds which do not necessarily indicate the presence of petroleum, although they may be present in petroleum, also fluoresce under ultraviolet light. Extracts of coals, coallike materials and chlorophylls all fluoresce under ultraviolet light but are not an indication of the presence of petroleum. Anthracene-type materials, for example, fluoresce with a light blue color and are readily extracted from soft coal and anthracite. Where the anthracene is oxygenated and occurs as anthraquinone, it also fluoresces Organic acids and cresols likewise contribute to the overall fluorescence of earth samples. Crude oils, however, contain much less of these materials than do shales, especially oil barren shales. If a sufliciently strong solvent is used to extract substantially all of the desired petroleum constituents, then any of these undesirable fluorescent organic constituents present in the sample will be extracted along with the desired petroleum constituents.

In copending application S.N. 94,168, a chromatographic separation method is used to separate from the earth sample those constituents which are not mobile in polar chromatographic carrier solvents but which are mobile in non-polar chromatographic carrier solvents. The fluorescence of these constituents is checked to determine the presence of fluorescent petroleum constituents in the earth sample. The desired separation is achieved, preferably, by a two dimensional technique in which a small quantity of earth extract is placed on chromato graphic adsorption material and driven in two different directions by two different carrier solvents. This two dimensional technique is suitable for the analysis of surface soil samples which contain about 0.1 to 10 grams of extract per kilogram of soil. When the extractable material is present in only trace amounts, at more sensitive method is needed. If a larger amount of soil extract is placed on the chromatographic paper used in the two dimensional technique, the spot tends to spread out masking the results obtainable when the extract is moved by the two different carrier solvents.

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It is an object of the invention to provide an improved method of geochemical exploration to determine the proximity of petroleum deposits.

Another object of this invention is to provide an improved method for detecting the presence of petroleum constituents in earth samples.

A further object of this invention is to provide an improved method for detecting the presence of petroleum constituents which may be present in trace amounts in surface soil samples.

The objects of this invention are accomplished by means of a paper strip chromatogram technique in which the evaporation of a greater amount of solvent extract on the chromatographic paper enables more hydrocarbons to be placed on the paper than is feasible employing the two dimensional technique. Preferably, a strip of chromatographic paper is immersed in a bottle containing the soil sample and solvent, or a measured volume of solvent extract, so that the solvent is carried -by capillarity up the strip and past the mouth of the bottle. The solvent evaporates as it is carried past the mouth of the bottle leaving a concentrated band of soil extract on the paper. Alternatively, the band may be placed on the paper by slowly dropping the solvent extract on the paper at a rate which 7 allows the solvent to evaporate before spreading over too much area. The evaporation of the solvent as it passes the mouth of a bottle is preferred since this method gives unattended, uniform evaporation and smooth deposition of extract. The band of soil extract may be spread out by means of various chromatographic carrier solvents so as to separate those constituents of the earth sample which are not mobile in polar chromatographic carrier solvents but which are mobile in non-polar chromatographic carrier solvents. The fluorescence of these constituents is thenchecked to determine the presence of fluorescent petroleum constituents in the earth sample.

In practicing the present invention, the earth sample being analyzed is first treated with a suitable solvent to extract organic constituents including the desired petroleum constituents therefrom. This extract is then placed in a bottle into which a paper strip is inserted. A relatively thin strip of material is preferred. Special chromatographic paper or ordinary filter paper is especially suitable for this purpose. The solvent is carried by capillarity up the strip and past the mouth of the bottle where the soil extract is concentrated by the evaporation of the solvent. When evaporation is complete, the soil extract exists as a band about half way up the paper strip. This band may be spread out or developed by treatment with selective chromatographic carrier solvents so that the various fractions may be isolated on the paper ready for analysis.

The concentrated band of soil extract is developed by dipping the very end of the paper strip into chromatographic carrier solvent contained in the bottom of a bottle. When the solvent front has moved up the paper by capillary action to a predetermined point, the paper strip is removed from the bottle and the solvent is allowed to evaporate. The solvents carry their mobile organic extracts at or near the solvent front, so the mobile bands can be placed quite accurately within a predetermined zone on the paper strip.

In developing the concentrated 'band of soil extract, various procedures may be employed. For example, the strip may first be immersed in a polar solvent which will, by capillarity, move the fraction of the organic material which is mobile in the polar carrier solvent. The strip is then cut between the original extract band and the polar mobile band. The strip containing the original band is then immersed in a non-polar carrier solvent which, by capillarity, moves the fraction which is mobile mensional chromatograms.

in the non-polar carrier solvent. The part of the original strip containing the polar mobile fraction is immersed in a non-polar carrier solvent so as to separate the fraction which is mobile in both a polar carrier solvent and a non-polar carrier solvent. Thus, the two portions of the paper contain the bands (1) polar mobile, (2) non-polar mobile, (3) polar mobile and non-polar mobile, and (4) residue, corresponding to the four corners of the two di- It should be understood that the concentrated band of extract on the paper strip may be treated first with either the polar orthe non-polar solvent. It has been found, however, .that somewhat sharper separations of various constituents are obtained when the polar solvent is used first.

A wide variety of organic solvents are suitable for extracting organic constituents from earth samples in the practice of the present invention. It is preferred, however, to use solvents sufficiently strong to insure that all of the desired fluorescent petroleum constituents are extracted from the sample. If all these constituents are not extracted, the quantitative analytical results will, of

course, be somewhat in error. To insure that substantially all of the constituents are extracted, the organic 'solvent used is preferably one which is sufiiciently strong to dissolve asphaltic material. These may be referred to as strong organic solvents. For this purpose asphaltic material may be defined as hydrocarbon material which is not soluble in pentane. Suitable strong solvents in clude, for instance, benzene, toluene, Xylene, carbon tetrachloride, di-ethyl ether, ethyl acetate, etc. -It has been found that combinations of strong non-polar solvents, such as benzene or toluene, with one or more polar solvents such as isopropanol, ethanol, methanol or acetone are particularly suitable. tion of isopropyl alcohol and toluene.

Likewise, any suitable polar and non-polar carrier solvents may be used in practicing the present invention. In order to cause all of the desired constituents to migrate without having an excessive amount of the relatively heavier ,asphaltic material migrate, it is preferred that both the polar and non-polar carriers be relatively Weak carriers which are not sufficiently strong to cause migration of asphaltic material as defined above. These may be referred to as weak polar and non-polar carrier solvents. Use of overly strong carrier solvents tends to cause migration of asphaltic material which then masks the presence of the desirable constituents, especially the lighter aromatics. Suitable we'ak pola-r carrier solvents include, for instance, methanol, ethanol, acetone or mixtures of these with small amounts of water.

Suitable non-polar carrier solvents include, for instance, straight chain hydrocarbons having at least 5 carbon atoms, branched chain paraflins, cycloparaffins, etc. Among the polar carrier solvents methanol has been found especially suitable While among the non-polar carrier solvents hexane, heptane and octane have been found especially suitable. I

The following compounds are typical of those which will be found in the various fractions isolated on the paper strip when the required chromatographic separation has been accomplished in the arbitrary manner described above using methanol as the polar carrier solvent and heptane as the non-polar carrier solvent.

Fraction mobile in polar and non-polar solvents:

authracene A preferred solvent is the combina-' 1,2 benzpyrene phenanthrene acenaphthene tetrahydropyrene I decalln 1,3,7 trlmethylnaphthalene:

(IJHa moOi) perylene acridine I pyrrole lndole dibenzothiophene H S cholic acid C Ha benzyldisulfidc: l CH3 naphthenic acids I C Hm-202 one example: HO- -0H ('30 OH 0 H3 progesterone: H 30 I C Ha C Hz C H3 C5-C1: parafiins Fraction mobile in polar carrier solvent but not in non-polar carrier solvent:

v :0 C II? I 2-naphtl1ol OH i cholesterol i CH3 l-naphtholc acid C OOH Y CHC HzCHs I C Ha (L H 2 A CH3 C H3 2-naphtl1oic acid HO C O OH stigmasterol:

C Ha CHs I quinoline: CHCH=CH CH OH; I meg J (3112 01-13 \N/ C nntluaqulnone O HO A p-toluidlne:

C Ha Y O carbazole I NHz methanol mobile heptane immobile fraction of crude roll 7 methanol mobile heptane immobile fraction of shale ex- H 7 5 tract Fraction mobile in non-polar carrier solvent but not in polar carrier solvent:

tetradecane 1 G Ha(C H2)12C Hz hexadecane CI-Ia(C H2)14C Ha etcosane C Ha(C H2) lsC Ha squalane C H; C H3 C H:

Aldrich Chemical: I

fiuoranthene:

3,4 benzofiuoranthene 1,12 benzoperylene fluorene clirysene trlphenylene cholestane:

CH: (3H2 CIICHzCHg CH3 l l E l 2% CH3 CH:

perhydropyrene Residue: I 3o p-terphenyl: I

coronene: 4O

Analysis of the separated fractions may be made by visual comparison to standards under ultraviolet light or by photometric methods using a fluorescence meter. For example, the strips may be compared against a crude oil standard under a high intensity ultraviolet lamp (3600 A.) and placing a value on each strip. Or, the fluorescence may be detected by a photoelectric cell which gives a reading on a voltmeter. Alternatively, the strips may be placed in bottles of solvent to redissolve the extract and measure, the fluorescence in solution using a fluorescence meter.

By applying the-chromatographic separation techniques described above to a number of earth samples takenfrom selected locations, it is possible to correlate the presence and quantity of petroleum constituents found in each sample with the location from which the sample was taken in order to determine the presence and proximity of petroleum deposits, such as reservoirs or petroleum bearing shale or sand, with respect to such location. For

the results to have relative meaning with respect to a number of samples from the same general area it is necessary only that the different samples be subjected to the same treatment. For the results to have any quantitative meaning it-is also necessary to have available comparative chromatograms based on known petroleum bearing formations. By preparing sets of standardized chromatograms using an arbitrarily standardized technique of vthe type described above and utilizing earth samples from known locations in reference to known petroleum deposits, it is possible to compare the fluorescence of the appropriate portions of the chromatograms obtained from the earth samples in question with the reference chromatograms in order to obtain quantitative data respecting the presence of petroleum deposits in the area from which the samples in question were taken. For best results fresh reference standards should be prepared at frequent intervals, preferably weekly, because the lighter aromatics in the fluorescent petroleum fraction exhibit decreasing fluorescence with time.

, The present invention permits the residue to be developed by means of somewhat more powerful solvents such as benzene, a benzene-heptane mixture, or a mixture of toluene and isopropanol, yielding a clear cut band of heavy hydrocarbon fractions. For example, in the procedure indicated above, the portion of the strip containing the original band and the non-polar mobile fraction may be immersed in benzene so that a benzene mobile fraction will separate from the residue by capillarity. It is advantageous, in some cases, to analyze the heavy hydrocarbon fractions as well as the other fractions in order to obtain a more complete evaluation of the sample. Also, the analysis of the benzene fraction alone has been used successfully to indicate the presence of petroleum constituents in surface samples. By lengthening the strip of paper and using a greater number of solvents, it would be possible to get more separations and more fractions for study and analysis. However, it is preferred to keep the steps at a minimum.

Example In order to evaluate the present invention, surface soil samples from a number of known formations were analyzed by the following procedure. In each case the surface soil sample was pulverized with a mortar and pestle so that all of the sample passed through a size 50 sieve (U.S. sieve series). Two grams of this material were placed in a small screw cap vial and two milliliters of a 1:1 solution of isopropyl alcohol and toluene were added with a pipette. The sample vial was then capped tightly, shaken vigorously for one minute and allowed to settle until the sediment was clear. This shaking procedure was repeated three times in 24 hours, after which the final settling occurred. 0.5 milliliter of soil extract were then drawn off and placed in a small vial, 35 millimeters high and 11 millimeters in diameter. A paper strip 8.5 millimeters by 70 millimeters was inserted in the vial. The solvent extract traveled up the strip by capillary action, and the solvent evaporated just past the vial top, leaving the extract in a concentrated band across and essentially midway on the paper strip. Approximately 0.2 milliliter of clean solvent were added to rinse the vial and flush traces of remaining extract up the paper to the concentrated spot. The paper was then removed and treated with the chromatographic carrier solvents in order to develop the fractions of the chromatograms. The paper strip was first placed in methanol which migrated past the band of soil extract separating those constituents mobile in methanol (polar carrier solvent). The strip was then cut between the original band of soil extract and the methanol-mobile fraction. The portion of the strip containing the methanol-mobile fraction was immersed in heptane in order to separate those constituents which are mobile in both the polar carrier solvent and the non-polar carrier solvent (heptane).

The portion of the strip containing the original band of concentrated soil extract was likewise immersed in heptane so as to extract those constituents mobile in heptane (non-polar carrier solvent) but immobile in methanol (polar carrier solvent). The residue was immersed in benzene in order to separate a benzene-mobile fraction.

The paper strips were then cut into their fractions and examined under a high intensity ultraviolet light (3660 A.). The intensity of the fluorescence of the fractions was noted and interpreted as described above. In the case of known oil bearing formations, the fluorescence of the fluorescent petroleum constituents was compared with reference standards prepared from related crudes. In addition, each of the surface soil samples tested was also tested in accordance with prior art techniques by examining the total extract from the surface soil sample under the same ultraviolet light.

When tested by mere examination of total extract under ultraviolet light as described above and suggested by the prior art, surface soil samples from the following regions which are known to contain little or no petroleum hydrocarbons exhibited strong fluorescence: eleven surface traverses in Noble County, Oklahoma; .two surface traverses in Vermillion Parish, Louisiana; and two traverses in Alberta Province, Canada. Further analyses of these samples in accordance with the present invention and as described above indicated, however, that the fluorescent constituents of these samples werenot petroleum constituents.

Surface soil samples from the following regions were also analyzed as described above: two additional surface traverses in Noble County, Oklahoma, and one surface traverse in Iberia Parish, Louisiana. In each case the extracts from these surface soil samples fluoresced strongly while analysis in accordance with the present invention disclosed that the fluorescent material was actually composed partly of fluorescent petroleum constituents and partly of fluorescent constituents not indicating the presence of petroleum. This is in accordance with known facts concerning these surface traverses. In the case of these earth samples, mere examination for fluorescence correctly indicated the presence of petroleum constituents but gave completely erroneous information concerning the relative quantities of such constituents since, except by the application of the present invention, it was impossible to determine how much of the fluorescence was attributable to petroleum constituents and how much to non-petroleum indicating constituents. When surface soil samples from these traverses were tested using the twodimensional c'hromatogram-luminescence analysis, no significant anomalies were apparent.

The above example indicates that the process of the present invention is capable of distinguishing between those fluorescent constituents of earth samples which indicate the presence of petroleum and those fluorescent constituents which may or may not be present in petroleum but which do not necessarily indicate the presence of petroleum. Furthermore, the greater sensitivity of the present invention enables analysis to be made of surface soil samples which contain only trace amounts of eXt-ractables for which significant results are diflicult to obtain using the two dimensional chromatographic technique.

While the invention has been described above in connection with certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be 'made without de parting from the spirit and scope of the invention, and it is intended to cover all such changes and modifications in the appended claims.

We claim:

1. The method for separating fluorescent petroleum constituents which are mobile in non-polar chromatographic carrier solvent and immobile in polar chromatographic carrier solvent from an earth sample containing the same which comprises contacting the earth sample with an organic solvent to extract organic constituents including the desired petroleum constituents therefrom, immersing a strip of chromatographic adsorption material in the solvent extract within an open-mouth container so that the desired amount of solvent is canried by capillari-ty up the strip and past the mouth of the container where the extracted organic constituents are concentrated by evaporation of the solvent and treating thus deposited organic material with a polar and a non-polar carrier solvent by first immersing the strip in one of the carrier solvents which will by capillarity move the fractions of the organic material mobile in such carrier, cutting the strip between original extract band and separated band, immersing portion containing original band in second of said carriers which will by capillarity move the fraction mobile in that carrier solvent.

2. The method according to claim 1 in which the earth sample is a surface soil sample.

3. The method according to claim 1 in which the organic solvent is sufficiently strong to dissolve asphaltic petroleum constituents.

4. The method according to claim 3 in which the organic solvent is a mixture of isopropyl alcohol and tolu 5. The method of claim 1 in which the polar carrier solvent is methanol and the non-polar carrier solvent is heptane.

6. The method of determining the presence of fluorescent petroleum constituents in an earth sample containing the same and other fluorescent organic constituents which comprises contacting the earth sample with an organic solvent to extract organic constituents including the desired petroleum constituents and other undesired fluorescent constituents therefrom, immersing a strip of chromatographic adsorption material in the solvent extract within an open-mouth container so that a desired amount of solvent is carried by capillarity up the strip and past the mouth of the container where the extracted organic constituents are concentrated by evaporation of the solvent and immersing the strip in a polar chromatographic carrier solvent which will separate from the deposited organic constituents by capillarity fractions mobile in said polar carrier, cutting the strip between the original band and separated fraction, immersing portion of strip containing original band in a non-polar chromatographic carrier solvent to thereby separate fractions mobile in the non-polar carrier solvent and subjecting thus separated fractions to ultraviolet light.

7. The method according to claim 6 in which the earth sample is a surface soil sample.

8. The method ofdetermining the presence of fluorescent petroleum constituents in an earth sample containing the same and other fluorescent organic constituents which comprises contacting the earth sample with a strong organic solvent to extract organic constituents including the desired petroleum constituents and other undesired fluorescent constituents therefrom, immersing a strip of chromatographic adsorption material in the solvent extract within an open-mouth container so that a desired amount of solvent is carried by capillarity up the strip and past the mouth of the container where the extracted organic constituents. are concentrated by evaporation of the solvent and immersing the strip in a weak polar chromatographic carrier solvent which will separate from the deposited organic constituents by capillarity fractions mobile in said weak polar carrier, cutting the strip between the original band and separated fraction, immersing portion of strip containing original band in a weak non-polar chromatographic carrier solvent to thereby separate fractions mobile in the weak non-polar carrier solvent and subjecting the separated fractions to ultra-violet light.

9. The method according to claim 6 in which the portion of the strip containing the separated fraction mobile in a polar carrier solvent is immersed in a non-polar carrier. solvent to separate the fraction mobile in both polar and non-polar carrier solvents from the fraction mobile only in a polar carrier solvent and subjecting these fractions to ultraviolet light.

10. The method according to claim 6 in which the residue of the original concentration of extracted organic constituents remaining after treatment with both polar and non-polar carrier solvents is developed by im-mersing the portion of the strip containing the residue in a somewhat more powerful non-polar carrier solvent than heptane so as to separate the fraction mobile in that solvent from the residue, and subjecting this fraction to ultraviolet light.

11. The method according to claim 10 in which the somewhat more powerful solvent is selected from the group consisting of benzene, a mixture of benzene and heptane, and a mixture'of toluene and isopropanol.

References Cited by the Examiner UNITED STATES PATENTS 2,431,487 11/1947 Larsen. 2,767,320 10/ 1956 Coggeshall.

MORRIS O. WOLK, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,254,959 June 7, 1966 Wayne S, Pallgatter et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, lines 2 and 3, for "assignors to Cities Service Research and Development Company, of New York, N. Y. a corporation of New Jersey" read assignors to Cities Service Oil Company, a corporation of Delaware line 12, for "Cities Service Research and Development Company" read Cities Service Oil Company in the heading to the printed specification,

lines 4 to 6, for "assignors to Cities Service Research and Development Company New York, N Y. a corporation of New Jerse read assignors to Cities Service Oil Company, a corporation 0 Delaware Signed and sealed this 1st day of August 1967.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. THE METHOD FOR SEPARATING FLUORESCENT PETROLEUM CONSTITUENTS WHICH ARE MOBILE IN NON-POLAR CHROMATOGRAPHIC CARRIER SOLVENT AND IMMOBILE IN POLAR CHROMATOGRAPHIC CARRIER SOLVENT FROM AN EARTH SAMPLE CONTAINING THE SAME WHICH COMPRISES CONTACTING THE EARTH SAMPLE WITH AN ORGANIC SOLVENT TO EXTRACT ORGANIC CONSTITUENTS INCLUDING THE DESIRED PETROLEUM CONSTITUENTS THEREFROM, IMMERSING A STRIP OF CHROMATOGRAPHIC ADSORPTION MATERIAL IN THE SOLVENT EXTRACT WITHIN AN OPEN-MOUTH CONTAINER SO THAT THE DESIRED AMOUNT OF SOLVENT IS CARRIED BY CAPILARITY UP THE STRIP AND PAST THE MOUTH OF THE CONTAINER WHERE THE EXTRACTED ORGANIC CONSTITUENTS ARE CONCENTRATED BY EVAPORATION OF THE SOLVENT AND TREATING THUS DEPOSITED ORGANIC MATERIAL WITH A POLAR AND A NON-POLAR CARRIER SOLVENT BY FIRST IMMERSING THE STRIP IN ONE OF THE CARRIER SOLVENTS WHICH WILL BY CAPILLARITY MOVE THE FRACTIONS OF THE ORGANIC MATERIAL MOBILE IN SUCH CARRIER, CUTTING THE STRIP BETWEEN ORIGINAL EXTRACT BAND AND SEPARATED BAND, IMMERSING PORTION CONTAINING ORIGINAL BAND IN SECOND OF SAID CARRIERS WHICH WILL BY CAPILLARITY MOVE THE FRACTION MOBILE IN THAT CARRIER SOLVENT. 